Food Microbiology
Introduction
Contents
• Introduction
• Taxonomy
• Detection methods, conventional
techniques
• Growth parameters, factors
• Food Spoilage
• Food Pathogens
• Food preservation methods
Food Microbiology
Microorganisms as causative agents
of disease in Humans--Foodborne
pathogens
Microorganisms and Food spoilage
Microorganisms as Food sources
Microorganisms used for the production of
food
Microbes and Agriculture
Food Microbiologist
Gain knowledge in the followings:








Determination of microbiological quality of foods
Uses of ingredients with appropriate techniques
Knowing sources of microorganisms contaminating with foods
Determination of microbial types involved in spoilage and
foodborne disease
Design correct procedures to control the spoilage and
pathogenic microorganisms in food
Design effective sanitation procedures
Effective use of desirable microorganisms to produce fermented
foods
Food regulations in food production
Scope of study in Food Microbiology
1.
2.
3.
4.
5.
BACTERIA--bacteriology
FUNGI--mycology
PROTOZOA—parasitology
ALGAE
VIRUSES--virology (although not a cellular entity but an
intracellular parasite)
6. WORMS—parasitology (helminthology) --not true microorganisms—but included in food/medical microbiology
7. PRIONS—pathogenic neural derived proteins
8. EPIDEMIOLOGY—study of the source and prevalence of
disease
History of
Food Microbiology
Image: Drawing of Death Bringing
Cholera in Le Petit Journal, circa 1912
the spontaneous generation of life Debate
 The belief in the spontaneous
generation of life from
nonliving matter was introduced
by Aristotle, who lived around
350 BC.
 According to Aristotle, it was:
“readily observable that aphids arise from the
rainfall which falls on plants, fleas from putrid
matter, mice from dirty silage.”
 This belief remained
unchallenged for more than
2000 years.
 Until…
Images: Aphids, Flagstaff Fotos;
Bust of Aristotle by Lysippus, Wiki
Aristotle: 384 – 322 B.C.
Spontaneous Generation Debate
Experiments on Flies
First to formally challenge the accepted belief of spontaneous generation.
Redi's Question: Where do maggots come from?
Hypothesis: Maggots come from flies.
Experiment: Redi put meat into three separate jars.
Jar-1
• Left open
• Maggots developed
• Flies were observed laying eggs on the meat in the open jar
Jar-2
• Covered with netting
• Maggots appeared on the netting
• Flies were observed laying eggs on the netting
Jar-3
• Sealed
• No maggots developed
Francesco Redi, Italian physician,
naturalist & poet, 1626 – 1697.
Images: Redi’s experiment , Unknown;
Fracesco Redi portrait. Wiki
Spontaneous Generation Debate
Anton van Leeuwenhoek : “Animalcules”
(Pronounced Lay-when-hook)
 As a tailor, used lenses to examine cloth. It
was probably this that led to his interest in lens
making.
 He assembled hundreds of microscopes, some
of which magnified objects 270 times.
 As he looked at things with his microscopes, he
discovered “micro” organisms - organisms so
tiny that they were invisible to the naked eye.
 He called these tiny living organisms
“animalcules”. He first described bacteria and
the protozoans.
Images: Leeuwenhoek portrait 1680, Jan Verkolje
(I);. Replica of Leeuwenhoek microscope, Jacopo
Werther; Man with scope, source unknown
1632 - 1723
The Controversy Over Spontaneous Generation
John Needham & Lazzaro Spallanzani
The Question:
What causes tiny living things to appear in decaying broth?
Needham’s Hypothesis: Spontaneous generation.
French
chemist
Louis
Pasteur’s
design of
this experiment settled
the argument.
Spallazani’s Hypothesis: Microbes come from the air. Boiling will kill them.
Needham >
1713 - 1781
Spallazani >
1729 - 1799
Image: Louis Pasteur, Pierre Lamy Petit circa
1866; Lazzaro Spallanzani, 1729-1799
The history of thermal
canning
•
His discovery of a food preservation process
occurred
•
He established a cannery and exported his products
to other countries.
Nicolas Appert
(1749–1841)
The Controversy Over Spontaneous Generation
Louis Pasteur & Industrial Microbiology
- Q: What is fermentation?
- What causes fermentation?
Some scientists thought that air caused fermentation
Others thought that microbes caused fermentation.
- Q: What is pasteurization?
Pasteur’s
Observations:
1. Blobs were alive because
they divide and make more of themselves.
2. Put grape juice + yeast in open and in
air-tight containers. Fermentation occurred
in both. This means that yeast are
_________ _________.
3. Took two flasks of sterile grape juice
and introduced bacteria into one and
yeast into another.
Are these non-living
blobs or living
microbes?
< yeast + grapes = yummy wine  (ethanol)
bacteria + grapes = spoiled wine  (lactic acid) >
Image: Louis Pasteur, Pierre Lamy Petit, circa 1866; Grapes fermenting;
Sachromyces yeast; Lactobacillus, Public health Image Library #1048
Louis Pasteur
• Old Theory: spontaneous
generation
– micro-organisms are the result of
decaying matter.
• New Theory: germ theory
– micro-organisms cause decaying
matter.
– Pasteur showed you could kill the
micro-organisms by applying heat PASTEURISATION.
• 61C for 30 min
The Germ Theory of Disease
Sherlock This…
 Oliver Wendell Holmes Sr. & Ignaz
Semmelweis - physicians practicing in
different parts of the world.
 Oliver Wendell Holmes Sr.(US)
Believed death following childbirth (puerperal fever)
often caused by the material on hands of midwives or
attending physicians.
1809 - 1894
 Ignaz Semmelweis (Austria)
Noticed death rates higher in maternity wards
staffed by medical students than in those attended
by midwives. Death rates decreased in summer.
Q: Why?
1818 - 1865
Images on right: Ignaz Semmelweiss, 1860
Jeno Doby; Oliver Holmes Sr., 1883
The Germ Theory of Disease
Importance of Hand Washing
Sung to tune of "Row, row, row your boat."
Wash, wash, wash your hands,
Play our handy game.
Rub and scrub, scrub and rub,
Germs go down the drain.
(Sing 2x = about 20 seconds.)
From the Virtual Microbiology Classroom on ScienceProfOnline.com
Images: Hand washing diagram, used
with permission © Clinical Skills Ltd
Meet the Microbe!
Organism: _______ ______
Streptococcus
Streptococcal Infections
Streptococcus is a Gram + cocci-shaped genus of
bacteria, which produce toxins that contributes to its
pathogenesis.
Some diseases caused by this bacterium include:
•
•
•
•
•
Puerperal fever
Strep Throat
Streptococcal Pneumonia
Scarlet fever
Necrotizing fasciitis (flesh-eating bacteria)
Images: Scarlet fever strawberry tongue Public Health Image
Library (PHIL) # 5120; Streptococcus pyogenes, PHIL #2110;
Necrotizing fasciitis, Smuszkiewicz, Trojanowska & Tomczak.
Germ Theory of Disease
miasma theory : Investigation of John Snow

Played key role in setting standards for good
public hygiene and preventing spread of
infectious disease.

Snow skeptic of the then-dominant “miasma
theory” (disease caused by bad air).

Believed cholera transmitted by water
contaminated with waste of other cholera
sufferers.

Mapped occurrence of cholera cases during
epidemic in London and found cases centered
around a specific public water supply.

Asked city of London to dismantle the pump.

Q: What do you think happened once water
pump was dismantled?
Images: Snow’s map of London, published by C.F.
Cheffins, 1854;. John Snow, 1813-1858, Wiki
1813 - 1858
Disease, Please!
Cholera
• Infectious gastroenteritis caused by the Gram
bacterium Vibrio cholerae.
• Transmission occurs through ingesting
contaminated water or food.
• Action on mucosal epithelium lining of the small
intestine responsible for the characteristic
massive diarrhea.
• One of the most rapidly fatal illnesses known.
• Progresses from first liquid stool to shock in 4
to 12 hours, with death quickly following without
rehydration treatment.
Image: Drawing of Death Bringing Cholera in Le Petit
Journal, circa 1912; Vibrio cholerae, PHIL #5324
-
The Germ Theory of Disease
Tyndallization: Discovery of : John Tyndall
 Discovered that some bacteria existed in two
forms:
1. heat-stable form (endospore)
2. heat-sensitive form (vegetative cell)
1820 - 1893
 Need prolonged or intermittent heating to
destroy the heat-stable endospores.
 His research resulted in a method of sterilizing
liquid by heating it to boiling point on successive
days, referred to as Tyndallization.
 Tyndallization is useful for sterilization of
growth media in science classes and other
situations where autoclaves not available for
pressure sterilization.
Images: John Tyndall; , H.B. Hall N.Y.
1878; Endospore stain T. Port
What Causes Gas Gangrene?
Meet the Microbe!

Most often caused by the endospore producing
Gram + bacteria, Clostridium, Streptococcus

Clostridium bacteria produce many different
toxins which can damage to tissues, blood cells, and
blood vessels.

Under low-oxygen (anaerobic) conditions,
Clostridium produces toxins that cause tissue
death and related symptoms.

Gas gangrene can also be caused by Group A
Streptococcus (Gram +) . And there are other
bacteria that can cause similar infections.

Gas gangrene most often occurs at the site of
trauma or a recent surgical wound. The onset of
gas gangrene is sudden and dramatic.
Images: Clostridium perfringens, PHIL #11196, Don Stalons;
Gas Gangrene, Schröpfer, Rauthe & Meyer, Wiki
Germ Theory of Disease
Robert KochTechniques
1843 - 1910
 Experimented with medium to grow
bacteria on.
 He tried gelatin, but it did not work.
 Wife of colleague recommended agar (a
gelatin-like product derived from seaweed).
 Didn’t melt, and bacteria couldn’t digest it.
 He could also add various nutrients
necessary to grow certain organisms.
 Koch (pronounced Coke) originated use of a two
part dish for growing bacteria (petri dish,
named after Julius Petri, a German
bacteriologist), and a technique for
isolating pure bacterial colonies.
Images. Micrococcus luteus colonies, T. Port; Robert Koch
portrait, 1843-1910, NIH; MAC differential media, T. Port
Disease, Please!
______________
Gram + Bacillus anthracis

An endospore-producing bacterium.
(Only the genera Bacillus & Clostridium
produce endospores.)

Bacillus anthracis first bacterium
proven to be the cause of a disease.

Anthrax was a disease killing European livestock. Farm animals,
apparently healthy in the morning, might die by the end of the day,
blood turned black.

Humans interacting with the animals were also at risk of becoming ill.

In 1877, Robert Koch grew Bacillus anthracis in pure culture,
demonstrated its ability to form endospores, and produced
experimental anthrax by injecting it into animals.

These experiments resulted in Koch formulating guidelines, called
Koch’s pastulates, for linking specific organisms with specific
diseases.
Robert Koch's original micrographs of the anthrax bacillus.
Image: Gram stained Bacillus anthracis, ,Public Health Image
Library #2105; Inhilation Anthrax in monkey spleen tissue, NIH.
Germ Theory of Disease
Koch’s Postulates
Germ Theory of Disease
Gram stain

First of Koch’s postulates demands that the suspected agent must be found in every case of a
given disease.

That means the tiny microbes must be seen and identified. However, in most cases, microbes are
colorless and difficult to see.

Christian Gram (1850-1938) developed a technique, the Gram stain, that is still widely used today.

Differential stain that involves the application of a series of dyes.

Leaves some microbes purple and others pink.

Microbes that stain purple, Gram-positive, and those that stain pink, Gram-negative.
Images: Gram positive and Gram negative bacterial stains, T. Port
The Germ Theory of Disease
Joseph Lister – Father of Modern Antisepsis
Prevailing belief = Wound infection due to tissue
exposed to stinking "miasma" in air.
Lister had read a paper by Pasteur showing that rotting could occur without
oxygen if microorganisms present.
1827 - 1912
Maybe microorganisms were causing gangrene?
Carbolic acid was used for deodorizing sewage, so Lister tried spraying instruments, surgical incisions,
wounds and dressings with solution.
It markedly reduced the incidence of gangrene.
As germ theory became more widely accepted, understood infection best avoided by preventing
bacteria from getting into wounds in the first place. This led to the rise of sterile surgery.
Image: Joseph Lister, circa 1860, Wiki
The Germ Theory of Disease
Proponent of cleanliness and antiseptic techniques

English nurse who was a proponent
of cleanliness and antiseptic
techniques to the field of nursing.

She came to prominence for her
pioneering work in nursing during
the Crimean War (say cry-me-in),
where she tended to wounded
soldiers.

She was meticulous about collecting
and analyzing data on her practices,
to provide proof of their efficacy.

Founded the Nightingale School for
Nurses, the first nursing school in
the world.
1820 - 1910
Image: Florence Nightingale from Carte de Visite, circa
1850; Polar area diagram by Florence Nightingale 1858.
Early History of Immunology
1749 - 1823
_____________ and the first _______

Was aware of farm workers' belief that if you had cowpox
in past, you wouldn’t get smallpox.

Cowpox caused mild discomfort, aching, a few pustules,
some swelling…symptoms that disappeared in a few days.

In contrast, smallpox caused massive disfigurement,
sometimes blindness, and often death.

Jenner, in the late 1700s, made small incisions or
punctures with cowpox material in arms of human subjects
in order to prevent smallpox.

At first his peers doubted the safety and efficacy of his
treatment, but eventually the value of the cowpox
inoculum was recognized.

Jenner’s works are said to have saved more lives than the
efforts of any other person in history.
Images: Dr. Edward Jenner by James Northcote;
Child with Smallpox, James Hicks, CDC
Early History of Immunology
Pasteur’s vaccinations

Individuals who recover from an infectious disease
sometimes immune from future attack.

Prompted Pasteur to try to find a way to prevent fowl
cholera in chickens.

Colleague of Pasteur’s postponed inoculations of cholera
into a group of chickens, a remarkable discovery resulted.

Inoculation with these neglected cultures made the
chickens immune to fowl cholera.

The microbes had been weakened or attenuated.

Pasteur also modified other organisms (anthrax and the
virus causing rabies).

Ultimately created inoculation procedures.
1822 - 1895
Image: Louis Pasteur, Pierre Lamy Petit, Frenchcirca
1866, Boy being vaccinated, PHIL #9364.
Discovery of Antimicrobial Agents
sulfa drugs
•
Dr. Gerhard Domagk (say Doe-mock), a
German chemist who discovered that
the dye Prontosil was effective against
a wide range of bacteria.
•
Won the 1939, Nobel Prize in Medicine.
•
Sulfanilamide portion of the Prontosil
molecule is responsible for its
antibacterial effect (sulfonamides = sulfa drugs).
1895 - 1964
Images: Dr. Gerhard Domagk, 1964,
Wiki, Sulfanilamide elixer, Source
Discovery of Antimicrobial Agents
penicillin

Alexander Fleming (1881 – 1955), a Scottish
biologist and pharmacologist, observed
bacterial staphylococci colonies disappearing
on plates contaminated with mold.

Fleming extracted the compound from the
mold responsible for destruction of the
bacterial colonies.

The product of the mold was named penicillin,
after the Penicillium mold from which it was
derived.

Nobel Prize in Physiology of Medicine in 1945.
From the Virtual Microbiology Classroom on ScienceProfOnline.com
Images: Penicillium mold, PHIL #8396; Staphylococcus aureus on
antibiotic test plate, PHIL #2641; Poster attached to a mailbox
offering advice to World War II servicemen, 1944, NIH